1. Field of the Invention
The present invention relates to a digital signal processing for such displays as a liquid crystal display and plasma display, and more particularly to a y correction circuit and a xcex3 correction method where the xcex3 correction of digital video signals is executed by line graph approximation.
2. Description of the Related Art
The relationship of the luminance value (X) of the video signal to be input to the display to the output luminance (Z) of the display is called the xe2x80x9cxcex3 characteristicxe2x80x9d, and the characteristic of a cathode ray tube display, which now dominates the market, is approximated as Z=kxc2x7X{circumflex over ( )}xcex3 (xcex3th power of X). Therefore in NTSC type television broadcasting, the xcex3 characteristic of a cathode ray tube display as an image receiver is considered and video signals are transmitted after executing reverse xcex3 correction at xcex3=2.2.
In the case of a liquid crystal display, on the other hand, the xcex3 characteristic is different from that of a cathode ray tube display, so if the television images and computer images created by a cathode ray tube display are displayed on a liquid crystal display, luminance reproduction will be distorted. To control the distortion of luminance, it is necessary to include a xcex3 correction circuit in the display so as to execute xcex3 correction on the input video signals at an optimum xcex3 value before displaying. However, a xcex3 value optimum for video signals is generally not always the same where xcex3=2.2 is used in the case of a television, and xcex3=1.0 is used to expressed the fine difference of gradation and colors when images are created by a personal computer. Also the xcex3 value is different depending on the cathode ray tube display, so in order to reproduce ideal luminance for computer images, it is necessary to execute xcex3 correction based on the xcex3 characteristic of the display used for image creation.
Therefore in order to display these input images with an optimum xcex3 characteristic, a line graph xcex3 correction circuit, which approximates the xcex3 characteristic curve with a plurality of straight lines and executes non-linear processing on digital video signals, is used, as stated in the Japanese Patent Laid-Open No. 8-18826.
Also as a xcex3 correction circuit control method, a display stated in Japanese Patent Laid-Open No. 7-152347 exists, where a plurality of sets of xcex3 correction data, such as slopes and intercepts, are prepared and a switching operation is executed by input signals.
Also as Japanese Patent Laid-Open No. 10-145806 states, there is a display which holds the plurality of xcex3 correction data separately for each R, G and B, and white balance adjustment is executed by the xcex3 correction circuit at the same time as xcex3 correction.
A conventional type xcex3 correction method will now be explained with reference to FIG. 2. In FIG. 2, 220 is a storage device for storing xcex3 correction data corresponding to n number of xcex3 values, such as a first xcex3 correction data 221, a second xcex3 correction data 222 and so on until the nth xcex3 correction data 223. 230 is a line graph xcex3 correction circuit. In the line graph xcex3 correction circuit 230, 231 is a decoder which outputs a signal to the line graph block for the input video signal data. 232 is a slope data selector which outputs a slope data, 233 is an intercept data selector which outputs an intercept data, 234 is a multiplier, 235 is an adder and 236 is a limiter which executes limiter processing on the video data.
210 is a xcex3 conversion section. A xcex3 correction selection section 211 reads one data from the n number of re-xcex3 corrected data in the storage device 220 based on the xcex31 value which was input. The calculation section 212 calculates the slope and intercept of each straight line of the line graph in FIG. 3 using the re-xcex3 corrected data which was read.
By storing xcex3 correction data having a target xcex3 characteristic in the storage device 220 in advance, optimum xcex3 correction is possible for a video signal having a plurality of xcex3 characteristics. White balance can also be adjusted by preparing the configuration in FIG. 2 for three colors: R, G and B.
With the conventional method, however, the correction data must be stored in the storage device for the assumed number of xcex3 characteristics and white balances, so an increase in the capacity of the storage device is indispensable to support the subtle changes of xcex3 values and white balance.
With the foregoing in view, it is an object of the present invention to provide a display which implements subtle xcex3 correction, and digital white balance adjustment, as well as black level and contrast adjustment by digital signal processing using the above line graph xcex3 correction circuit and a small capacity storage device.
To solve the above problems, the display of the present invention has a xcex3 correction circuit for correcting digital video signals by line graph approximation, where the storage device holds a xcex3 characteristics of the display device, and video signals being input are displayed at the desired xcex3 characteristics, black level, contrast and white balance using a micro-controller, which calculates the slope and intercept of the line graph by the xcex3 characteristic of the display device, data which was input by the xcex3 value input means, white balance input means, black level input means, and contrast value input means, and the ideal xcex3 curve, and sets the slope and intercept of the line graph to the xcex3 correction circuit.
A first aspect of the present invention is a xcex3 correction circuit for executing reverse xcex31 correction on pre-xcex31 corrected input video data and then executing xcex32 correction, comprising: means for setting a representative luminance value; primary conversion means for executing reverse xcex31 correction on the representative luminance value so as to generate a primary conversion value; secondary conversion means for executing xcex32 correction on the primary conversion value so as to generate a secondary conversion value; means for generating a slope and intercept of each straight line of a line graph which pole is the secondary conversion value; and line graph xcex3 correction means for executing xcex3 correction on the input video data by the line graph.
A second aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a xcex31 value.
A third aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a xcex31 value and a black level value.
A fourth aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a xcex31 value and a contrast value.
A fifth aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned primary conversion means receives a xcex31 value, a red adjustment value, a green adjustment value and a blue adjustment value.
A sixth aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned secondary conversion means has a table denoting a relationship between pre- xcex32 correction and post xcex32 correction.
A seventh aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned y1 value is a xcex3 correction value for a cathode ray tube display.
An eighth aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned xcex32 correction is a xcex3 correction for a liquid crystal display.
A ninth aspect is a xcex3 correction circuit according to the first aspect, wherein the above mentioned xcex32 correction is a xcex3 correction for a plasma display.
A tenth aspect is a xcex3 correction method for executing reverse xcex31 correction on pre-xcex31 corrected input video data and then executing xcex32 correction comprising steps of: setting a representative luminance value; executing a reverse xcex31 correction on the representative luminance value so as to generate a primary conversion value; executing xcex32 correction on the primary conversion value so as to generate a secondary conversion value; generating a slope and intercept of each straight line of a line graph which pole is the secondary conversion value; and executing xcex3 correction on the input video data by the line graph.